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The only criteria for a petrol engine to run on LPG is that the engine needs to be unleaded friendly as there is no lubrication available with LPG. Therein lies the problem running a diesel on it because a diesel needs the 'oilyness' of diesel fuel to provide lubrication to the engine and injector pump. Otherwise a diesel will run perfectly well on LPG but there will be little or no gain in MPG. Cost of fuel may be less.

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Col

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The only criteria for a petrol engine to run on LPG is that the engine needs to be unleaded friendly as there is no lubrication available with LPG. Therein lies the problem running a diesel on it because a diesel needs the 'oilyness' of diesel fuel to provide lubrication to the engine and injector pump. Otherwise a diesel will run perfectly well on LPG but there will be little or no gain in MPG. Cost of fuel may be less.

I'm confused. What does unleaded have to do with lubrication?

Lead was added in the form of Tetraethyl Lead to prevent 'knocking' or 'pre ignition' . 'Unleaded' engines overcome this through different ignition timing AIUI. They still rely on oil for cylinder lubrication.

Col

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I didn't mention any political persuation !

You don't have to Mick. Public policy and the spending of public money are by defintion, political issues. Party positions don't need to be mentioned.

I'm not taking sides in this debate though except to say one thing.

The value of any system of public transport cannot, IMHO be determined on a simple profit/loss basis. This because much of the real value exists in the 'lubrication' of the whole 'socio economic' environment. In other words, without public transport, the economy is far less efficient.

Even the Americans.. arch capitalists.. recognise the need for public funding for some transport. The US government heavily subsidises Rail and Air transport, as well as the Interstate Highway system.

Col

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Tetraethyl Lead was also added to petrol not JUST to prevent knocking but also to prevent excessive wear to valves and valve seats particularly exhaust valves. It is nothing to do with cylinder lubrication. I have a 1971 Rover 2000TC. The exhaust valves are Nimonic 80A (Basically Jet heat) which is fine with unleaded but the valve seats are not suitable with unleaded (they are cast iron in an alloy head) so without the tetra lead in the petrol or a suitable additive I get valve seat recession. This engine IS NOT suitable for LPG conversion as there would be no lubrication for the valve seats.

As an aside when I was using that car as my daily transport I got 22,000 miles out of a cylinder head until my tappet clearances disappeared. I just stuck another cylinder head on and off I went again. It is now on its third cylinder head but as these things are no longer as readily available as they were I shall have hardened seats fitted to the cars original head which I have retained and continue carry on as normal.

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But it was you who mentioned lubrication! :)

engine needs to be unleaded friendly as there is no lubrication available with LPG.

You are correct that the leaded petrol also reduced excessive exhaust valve wear, but as I understand it, the excessive wear was itself caused by the knocking. In effect, the closed valve took a 'hammering' so severe that it 'micro welded' to the seat which caused progressive damage as the valve opened, closed, welded, opened etc. So, cure the knocking and you cure the wear.

That's my understanding anyway. But, I could be wrong. (This is a very rare occurrence, but has been known.. :) ) I'm trying to establish whether the lead provided any 'direct' protection to the valves, in addition to preventing knocking. If it did, I'm wrong, and happy to admit it.

Col

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The valves spin as they seat. As in they don't just open and shut. The tetra lead prevents wear as they seat. Knocking occurs on top of the piston.

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Knocking exerts equal force on all components enclosing the combustion chamber. It cannot be otherwise, because the 'knock' or explosion occurs within a gas, and gases under pressure exert equal force at all points. So, whilst much of the noise may be transmitted, or generated by a rattlng of the piston/pin/con rod/ big end assembly, there is also a knock which hits any closed valve and can cause microwelds.

Not heard about the spinning valves, but I'd be interested to know what mechanism causes it.

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Old, but informative.


Lead and Lead Substitutes - The Facts
The lead in petrol is known as Tetra Ethyl Lead (TEL) or Tetra Methyl Lead (TML) and was originally developed
in the 1920’s by a joint venture between General Motors and Standard Oil (now known as Exxon - Esso in
Europe).
The original reasons for adding lead in petrol was not to prevent Valve Seat Recession (VSR) but to raise the
octane of the petrol. This octane gain allowed engine designers to increase compression ratios and hence
power without any dangers of engine damage. These more modern high compression engines were now able
to run at higher revolutions without experiencing knocking or pinking.
Before the development and introduction of lead to fuel, engines were successfully run without lead, albeit
at low compression ratios which gave low power and low fuel economy. As engines of the period were not
highly stressed valve seat recession did not appear to be a major problem.
The world-wide use of lead and the discovery that lead compounds formed during the combustion of lead
alkyls prevented valve seat recession (VSR) by forming thin layers of lead oxides and sulphates on critical
valve/seat interfaces was a bonus. This led to the world-wide practice of machining valve seats directly into
the cast iron head.
Problems occur with these engines once lead is removed from the petrol and the protection is lost, which is
when recession starts. The combustion of the petrol in the cyliders generates extreme heat on the exhaust
valve seats as the burnt gases pass through. Each time the valve is hammered open and shut, it momentarily
welds itself to the valve seat at the hottest points. This localised welding of the exhaust valves to their seats
tends to be followed by ‘tearing out’ of small fragments of metal from the seat, ie. the valve sticks to its seat
and as it is lifted off by the valve gear, it ‘rips’ away from its micro-welded condition. Small particles of valve
seat material are thus embedded in the valve face and are likely to be further oxidised forming ‘warts’ of hard
iron oxide.
The continuous repeated impact of these hard materials on the soft valve seat causes further damage and,
if the valve seat rotates, a degree of ‘grinding in’ will also occur. From this moment on, valve seat wear is both
rapid and inexplorable leading to engine failure as the valve and seats burn away.
Other than the actual material from which the valve seat is made, the next most important factor in determining
whether VSR will take place, is the driving condition. All the technical data produced indicates that engine
speed and load are significant factors. VSR has been found to be an exponential function of speed but the
relationship with engine load is believed to also be a factor.
The actual occurrence of VSR is related to seat temperature which increases with speed and load 9eg.
acceleration, climbing hills, motorway driving and towing).
The demise of lead from petrol which is set for 1st January 2000, (but will probably become more and more
difficult to find from mid 1999), will cause premature failure to those engines which have ‘soft’ valve seats
when used under modern road conditions. Competition use, continental touring and high speed driving will
exacerbate the problem.
Development and Testing
It is widely accepted that lead is the best material for VSR protection and octane response when used at the
UK maximum permitted treatment of 150 mg/ltr. Typically however, the current BS 4040 4 star leaded fuel has
a concentration in the range of 80-120 mg/ltr or a minimum lead content of 50 mg/ltr. So what are the options
for owners of pre 1990 and classic cars and how are these verified?
Additive Chemistry
The move to unleaded petrol around the world stimulated the development of additives to prevent VSR. The
research has led to the availability of several technologies all of which are based on metallic salts:
Sodium
Potassium
Phosphorus
Manganese
Metal Pellets
Sodium
This type of product was one of the initial materials tested in the US when Pb levels in leaded gasoline were
reduced to 26mg per litre. Because of these moves a programme was run jointly by the US Environmental
Protection Agency (EPA) and the US Department of Agriculture (USDA) on two basic chemistries, Sodium being
one.
Testing in various engines showed that at the recommended treatment some degree of protection against
VSR was provided. However, at four times the recommended treatment VSR was eliminated. A negative finding
during the testing was that oil black deposits were found in the inlet tracks.
Sodium is also known to form low melting point eutectics in very hot regions. This is known to result in erosion
problems, particularly with turbochargers. As a consequence of these findings, Sodium has been withdrawn
from the list of chemistries being considered for use in Lead Replacement Petrol (LRP).
Phosphorous
This material was also included in the original EPA/USDA study. The treatment was tested at about double
the recommended treatment and reduced VSR although a wear rate value of 0.022ins/100 hours still signifies
future problems.
Additionally, this additive caused deposits to form in the inlet valve area of the engine to the extent that one
valve was unable to close fully and was starting to burn at the test completion - 200 hours.
In these tests the fuel treatments (Sodium/Phosphorous) were found to contaminate the crankcase oil. Such
contamination has a deleterious effect on the oil normally causing it to thicken. Phosphorous is also known
to be a severe poison for catalytic converters which could cause additional problems if mis-applied when
filling a car with petrol.
Potassium
With the demise of Sodium, Potassium has become its natural replacement since test work has shown that
Potassium will provide similar levels of VSR protection to Sodium. There is a large body of evidence which
demonstrates that potassium in the presence of lead alkyls or associated halogen chemistry scavengers leads
to inlet valve burning. While leaded fuel is still available any mis-fuelling and the use of after treatments
containing this type of product will remain a concern.
Potassium as a fuel additive has been previously used, not as a VSR treatment but as a fuel performance
enhancer. Many motorists may possibly recall the major problems which many cars, and the models of one
major car producer in particular, encountered when their cars were run on a well known brand of petrol.
Metal Pellets
There have been claims over many years that using metal pellets either in the fuel tank or fuel lines reduces
VSR. One such device which uses tin pellets was tested and reported in a Classic Car magazine in 1989/90
period.
The published results indicated that VSR protection was not achieved which is hardly surprising since the
solubility of metallic tin or lead in petrol is very low, in the order of one part in 10 million (VSCC !((!). This is
in contrast to the 30-50ppm of lead concentration generally considered as the minimum for protection.
Manganese
Manganese in the form of Methylcyclopentadienyl Tricabonyl (MMT) has been used in virtually all Canadian
unleaded petrol without any problems for well over 20 years. Its original use was for the self same reasons
that lead was first used - namely to increase octane.
Like the lead it can replace, MMT also protects soft valve seats from recession so it can be said that MMT is
the closest alternative to lead.
With MMT being available since the early 1970’s it has been subjected to the most vigorous testing of any fuel
additive in history with extensive test data to support its important feature:
Helps reduce intake valve deposits in conjunction with fuel detergents.
Does not contribute to valve stick either alone or in combination with detergents.
Completely safe in turbo-charged engines.
No adverse engine deposits formed.
Compatible with all construction materials including plastics and elastomers.
Insoluble in water preventing any interaction problems.
MMT has gained US EPA Waiver for use in unleaded gasoline along with Pipeline distribution approval due
to its non-surfactant properties.
Toxicity of VSR Materials
Any product which is added to fuel to be burnt in engines and expelled through the exhaust will have an effect
on emissions. Of all the treatment chemicals examined, only MMT has been subject to in-depth studies. These
have shown that no problems are posed in respect of emissions, hence the approval of US EPA.
For catalytically equipped vehicles statistically significant reductions in carbon monoxide (CO) and oxides of
nitrogen (NOx) have been observed.
Manganese is a naturally ocurring element found in soil, water, food and all living organisms. In the combustion
process the Manganese forms Manganese Oxide (Mn3 O4) and only about 0.1% Manganese is emitted from
the exhaust. Very high concentrations of Manganese (30,000 mg/m
3
) can have side effects (Parkinson like
symptoms) but a recent study conducted by Research Triangle Institute in Toronto, Canada, showed that no
citizens of that city are even exposed to the safe recognised scientific level which is set at 0.025μg/m
3
.
Little or no toxicology data is available for other metallic systems but it is considered that phosphorous
compounds can lead to highly toxic emissions similar in nature to organo-phosphates which are highly toxic
ie. Gulf war syndrome and the use of sheep dip on farms.
So how do we prevent Valve Seat Recession in most pre-1990 and Classic Cars?
It depends on how long you wish your car engine to last. You can retard the ignition and lose power and then
drive your car at very low speeds; never accelerate quickly, slow down when climbing a hill and always
decelerate immediately the engine starts to ‘pink’.
Your engine may last several years more, but it is a potential risk. Speed and higher engine temperatures will
severely damage the valve seats when running on unleaded petrol.
Can I have the soft seats replaced with hardened valve seats?
It is possible to replace valve seats in aluminium cylinder heads by machining out the old soft seats and
replacing them with hardened seats. However, with cast iron heads it is sometimes impossible or excessively
expensive to do so. The cost for valve seat replacement in aluminium or cast iron cylinder heads can be several
hundred pounds for a 4 cylinder engine and 2, 3 or 4 times that amount for V6’s, V8’s or V12 engines.
Even then you will still have to retrd the ignition to prevent pinking because 4 star leaded petrol is 97 octane
whereas premium unleaded is only 95 octane. Consequently you will lose power unless you use an Octane
Booster. If you retard the ignition by only 2 degrees you could lose in the region of 5% power at the wheels -
more degrees lose even more power. Remember as engines build up deposits with use, there is a requirement
for increased octane.
Will the oil companies offer a lead substitute petrol on their forecourts?
Prior to and after January 2000 some petrol companies may provide a lead substitute fuel at selected filling
stations. (One has already stated they won’t and older cars should be driven off the road). It is likely to be
expensive due to the low demand and the protection given to valve seats may be lower than required for high
engine load conditions. The lead substitute content of the fuel is expected to be low to prevent accidental
cross contamination of fuels at filling stations as some types of lead substitute fuels will severely damage
the modern catalytic converter equipped cars or to avoid any problems from sticking inlet valves.
Are lead substitute fuel additives the answer?
In many countries where leaded petrol is banned, bottled lead substitutes are on sale at filling stations. A
number of alternative lead substitute fuel treatments have been developed for this application but at the
present time these have potential drawbacks.
Millers VSP Plus, Lead Substitute and Octane Booster - Endorsed by the FB HVC
Millers VSP Plus is different, being based on proven manganese additive technology with US Environmental
Protection Agency (EPA) waiver for unleaded gasoline.
Millers VSP Plus treatment utilises MMT additive chemistry which mimics the properties provided by lead. It
gives a protective lubricant film on valve faces and seats while also increasing octane by 2-3 numbers,
something which other treatments have difficulty in acheiving in a single treatment.

Col

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Nobody made you read it! :laugh:

Col

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But it was you who mentioned lubrication! :)

You are correct that the leaded petrol also reduced excessive exhaust valve wear, but as I understand it, the excessive wear was itself caused by the knocking. In effect, the closed valve took a 'hammering' so severe that it 'micro welded' to the seat which caused progressive damage as the valve opened, closed, welded, opened etc. So, cure the knocking and you cure the wear.

That's my understanding anyway. But, I could be wrong. (This is a very rare occurrence, but has been known.. :) ) I'm trying to establish whether the lead provided any 'direct' protection to the valves, in addition to preventing knocking. If it did, I'm wrong, and happy to admit it.

Col

Comes to summat when you are quoting yourself. But I assured Pianoman that I would admit it if I was wrong.

It seems I was wrong. :sorry: Valves do indeed turn. From what I can gather it is not a deliberate thing but a function of the forces involved etc. But , nothing is done to stop it.

Also seems the lead in petrol does afford some sort of lubrication/protection to 'soft' valve seats, but not needed for anything much other than old direct cut seats in Iron heads.

I'm going into the garden to eat worms.... He said... Graciously...

Col

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Sorry I didn't get back to this as a result of doing something else. As I understand it the valve turns as it moves its length of travel with the opening and closing movement of the valve spring. A coil spring is a torsion bar coiled up and as a coil spring is compressed the wire it is made of also twists. I am saying no more on the subject purely because that is about as far as I went in my research to find out which car will and will not run on unleaded petrol and why.

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  • 3 weeks later...

Is the bloke to the right of the bus with his back to the camera having a pee up against the wall? 

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Just looking again at the bloke to the right of the bus.  I wondered what he was standing on, but close inspection appears to show he was standing on one of the large 'coping' stones from the top of the wall in front of him.  Somehow a couple of stones have been dislodged and he's standing on one to look through the gap.  Could be looking at the railway I suppose.

 

I don't remember that gap.  Is the wall still there since the area was re-developed for access to Tesco etc?  I can't recall, but if the wall is still there it would be interesting for someone to have a look when passiing to see if there are signs of repair.

 

Edit:  Hve a look at this Google Maps image:  https://www.google.co.uk/maps/place/Highbury+Rd,+Nottingham+NG6+9AT/@53.0002226,-1.1953327,3a,75y,352.59h,82.82t/data=!3m7!1e1!3m5!1sDFnk53oAAk-Wnr3iYJjKoQ!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DDFnk53oAAk-Wnr3iYJjKoQ%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D215.85739%26pitch%3D0!7i13312!8i6656!4m5!3m4!1s0x4879c1d2c17529f3:0x446124c3377c74fd!8m2!3d52.9956118!4d-1.1913038

Seems to show the same wall with a more recent repair from about the same point.

 

I'm confused though.  He seems to be at Spring Lane, so the railway would be behind him between Spring Lane and Church Lane..... or summat.. :wacko:

 

And yes MI, I reckon that car could well have been one of Eric's.    On that subject, I recall the young science teacher Steele,(the one with the albino streak in his hair) had a mini. (Mini Van I think)  Somebody had a Standard summat or other (Standard 8?) and Bert Dodd had a blue BSA Bantam.

 

Col

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DJ360 - yes, the man is standing on the corner shown in the Google Maps image. My first thought was also that he might be trainspotting, then I realised the railway is below where the photographer is standing.

 

I remember Eric Shepherd did have a car at least similar to that one - a Wolseley? Austin? (others will know). In my earlier days at High Pavement (1961/62) I used to get the no. 6 bus to school from the stop on Hucknall Road near to Haydn Road, and if Eric saw High Pavement boys waiting there he would usually stop and give us a lift. It was sometimes that one or more usually his little old Baby Austin (ANG732???).

 

The name Steele seems vaguely familiar but I can't bring him to mind. I think it was Bloom (John?) who had a Standard 8. The only other masters' car I remember is Ray Caulton's Standard estate which had all the foreign 'Tiger in Your Tank' stickers on it. 

 

 

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You got me there MI.

 

I recall that the Standard car had the little 'two flag' badge somewhere on it.  It was greyish.  That's al I recall.

 

Bloom. Yes, Curly haired chap I think.  Didn't he teach Physics?

 

This memory loss is a bugger...

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#4119

I  think  he appears to be standing on something, but not having a "Jimmy"

There appears to be some bricks missing off the top of the wall and our man looks like he is standing on them?

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The chap is looking into what is now the car park behind Wilkos. The little road to the right leads to the Argos car park and ultimately Tescos car park. The railway / tram tracks ar behind the man.

Ill check on the brickwork next week. 

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